Several centuries before there was any debate about the role of women in combat, Antonio Vivaldi tackled the issue head-on with his dramatic oratorio "Juditha Triumphans." Nicholas McGegan and the Philharmonia Baroque Orchestra gave the piece a fascinating, if uneven, performance in Stanford's Bing Concert Hall on Wednesday night, as the final offering of their 2013-14 season.

Sure, the biblical story from the Apocrypha already had one female warrior at its center - that would be Judith, the Israelite widow who saves her compatriots by hacking off the head of the invading Assyrian general Holofernes (Philharmonia's program insert reprints Caravaggio's unforgettable painting on the subject). But it was Vivaldi, writing around 1716 for the all-female conservatories of his native Venice, who gave the thing a purely female slant.

The result is a striking blend of familiar Baroque convention - the drama emerges in much the same series of formal arias and plot-laden recitatives that shape the operas of the period - and the surprisingly offbeat. The libretto is in Latin rather than Italian, and there is stateliness to the piece that sits oddly alongside its ferocious trumpet-and-drums militarism.

Yet there is no mistaking the theatrical fervor that infuses the score, and Wednesday's performance, populated by a fine quintet of singers and punctuated by brilliant instrumental turns from the orchestra, left a listener glad to make the piece's acquaintance.

Still, a brief consumer advisory is in order. Although the score of "Juditha" boasts some vibrantly inventive writing and innovative orchestral touches, these are concentrated almost exclusively in the second half. So the many patrons who skipped out of Bing at intermission were making an understandable but imprudent decision.

Until that point, the performance had consisted mostly of stolid, straightforward arias with an occasional noteworthy touch - a rich violin obbligato during one aria, or a particularly ingratiating vocal melody in the aria "Sede, o cara," in which Holofernes invites Judith into his tent.

But it's not until the second half that Vivaldi pulls out all the stops. Now we get a philosophical aria for Judith accompanied by mandolin alone (along with a few delicate string pizzicatos); a couple of gloriously spooky arias for Holofernes, one of them accompanied by dark-hued oboe and organ; and in a wonderful coup, the sudden appearance of a consort of viols to presage the bloody climax.

The performers, too, stepped up their game as the evening progressed.

Cécile van de Sant's Judith, marked by luminous vocal tone and fluid phrasing, sounded even more arresting toward the end of the performance than at first. As Holofernes, Diana Moore combined military grandeur and suave seductiveness into a superb portrait of a warrior at play on the fields of love.

In an elaborate show of symmetry, each of the principal characters gets a sidekick. Vivica Genaux, as Holofernes' squire Vagaus, struggled to be heard through the first half but came through at last with a magnificent account of her blazing final showpiece. Dominique Labelle - the only soprano in a world of mezzos - sang brightly as Judith's handmaid Abra, and Virginia Warnken swooped in at the end to bring closure as the local priest Ozias. The Philharmonia Chorale made fine appearances as Israelites and drunken soldiers.